"no good reason", except the performance, battery life & build quality?

Different people have different needs, preferences & ideological beliefs to you. If you measure the actions of others, based on your viewpoint alone, you will never understand the rest of humanity.

The biggest lesson that owning a Macbook has taught me is that my world view as a power user is a minority and worthless one that should be relegated to /dev/null under most circumstances.

Fucking nobody cares about the gripes I would have with it, and I've even come around to appreciate the fact that Apple sells goods engineered to the desires of people who aren't me (read: the majority): I can't deny the speakers on my Macbook are fucking amazing, and most people would care about that rather than whether something is FOSS.

Ok, but apart from the performance, the novel hardware architecture, the battery life, the build quality, the recyclability, and the documentation and tooling for developing custom kernels, what has Apple ever done for us?

Apple being more open would improve performance in certain applications, though.

I would love to have some examples, have you got any? Or is it just a feeling you have, that justifies your personal preferences?

What do you mean, it is pretty obvious that having more low level control would allow developers improve aspects of their software in certain cases. I am using software for some very time sensitive applications, and in this case linux > windows > macos just because apple's documentation and implementation is not dev friendly while linux with open source amd drivers have the best performance of all. Being closed and not dev-friendly has its costs, too.